This is pretty amazing: astronomers have determined the mass of the supermassive black hole in the center of the giant elliptical galaxy M87, and found it to be a crushing 6.6 billion times the mass of the Sun! This makes it the most massive black hole in the nearby Universe by quite a bit. And the coolest part is that they measured it by observing the speeds of the stars in the center of the galaxy as they orbit the black hole. That’s an incredibly delicate observation to make, and it took the giant Gemini telescope to do it, as well as considerable modeling of the galactic structure.

M87 is the central galaxy in the Virgo cluster and is 60 million light years away (so we’re not in any danger from it). The supermassive black hole in the center of our own galaxy is 4 million solar masses, so the one lurking in the core of M87 is 1600 times more massive than ours. Yikes. Also, M87 is bright enough to be seen with a relatively modest pair of binoculars from a dark site, so next time I get a chance I’ll have to take a look. Knowing such a monster lives there will make it even better to observe.

Red dwarf stars are the most common type of star in the Universe: smaller and cooler than the Sun, for a long time it was assumed they weren’t terribly active in any way. Decades ago, though, it was found they could emit tremendous bursts of energy, super-solar flares that put to shame what the Sun does when it’s active. Astronomers used Hubble images to look at over 200,000 red dwarfs, and caught 100 of them in the act of flaring. Some of these stars are pretty old, which is surprising, since it was thought they’d calm down with age. They might in general, but some seem able to stay peppy. My pal Nicole has more info about this on Discovery News.

The idea is that when big galaxies collide and merge, their central black holes will eventually merge as well. But first they have to approach each other, go into mutual orbit, and over millions or hundreds of millions of years, merge into one bigger black hole. A few binary pairs have been seen before, but this is the largest such group found systematically. The astronomers picked 50 galaxies with features that might indicate binary black holes (such as double sets of features typically seen in spectra taken of galaxies with supermassive black holes in them), and found 16 such pairs. The other galaxies without binary black holes may have something else going on in their cores; perhaps the black hole is producing beams of energy that are interacting with matter around them, for example.

What this means is that bigger telescopes with higher resolution will be able to separate even closer binaries, and eventually we’ll be able to sample a population of them all the way up to when they’re about to actually merge and combine into a single black hole. That must happen in all big galaxies, and has happened in ours perhaps many times!

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So how massive does a black hole have to be before it becomes a super-mega-ginormous black hole, with so much gravitational pull that not even gravity can escape?

That was a joke, but as a serious question: There is a threshold, if you will, where an ordinary object (like a star) can become sufficiently massive and dense to become a black hole. Are there any thresholds beyond that, either observed or theoretical, where a black hole can become so massive it changes into something else again? Or is there no theoretical limit to the size of a black hole?

Black hole mergers would likely play hell with any life bearing planets within those galaxies, especially if such a merger occurred such that the axis of rotation of the pair pointed through the ecliptic of the galaxy. Talk about a really big gamma ray burster,,,it could make the average GRB look like a firecracker next to a nuke.

@Robert: Yes (almost) any object can become a black hole if it’s dense enough, for example compressing the mass of the moon down to ~0.1mm will bring the escape velocity high enough to make it a black hole. You need a certain minimum mass called the Plank mass (around 21 ug) to make one due to quantum mechanics. Any object at least that massive has a Schwarzschild radius (size of event horizon) of R=2GM/c^2. There’s also been talk that according to some theories the LHC will generate extremely microscopic black holes but the these would evaporate almost instantly due to Hawking radiation. AFAIK there are no currently known limits to their size.

@Gary: Agreed. I hope we’re not staring down the axis of any of these mergers!

Red dwarf flares may seem extreme but some studies at least suggest that they may not be the kind of lethal problem that is usually assumed. This is thanks to the atmospheric chemistry of a planet responding to the large increase in ultraviolet radiation: in fact flares might even help to start biological processes via photochemical reactions.

I recall reading about the most massive black hole detected to date. I am fairly certain that they said it is a binary pair (one REALLY big one, and one somewhat dinky one). When they merge, it would be a 18 billion mass black hole.

That frightens me a tad to think about even though it is in a quasar almost at the edge of the visable universe.

How exactly do black holes ‘merge’? Supposing we have a supermassive one and a primordial one orbiting it.
Does the primordial one get ripped to pieces when it enters the supermassive bh’s roche-limit? Does madness ensue when the two event horizons ‘touch’?
What would the supermassive bh’s accretion disk look like while there’s a primordial blackhole zipping through it at close to the speed of light?
Would the primordial bh get spaghettified?

Blackholes are supposed to be pointmasses (singularities), so if our mathematical representation of a blackhole is correct and all the mass is indeed confined within a single point, then spaghettification should not occur. Nor should the less massive blackhole desintegrate by tidal forces. So another test of the singularity model should be that these effects are not observed, right?

Actually, the ONE SMB of that pair (designated OJ 287, located about 3.5 billion light-years away, only about 25% of the way to edge of the observable universe) is already (albeit tentatively) estimated to be about 18 billion solar masses. The other one orbiting near it with a period of about 11 or 12 years has a much lesser mass of perhaps 100 million solar masses, but it still qualifies as a supermassive black hole. (If the estimates are correct, it would be 25 times more massive than our own Milky Way’s SMB, but only 1/180 as massive as the primary). So the 18 billion solar mass will grow modestly when they merge in about 10,000 years, acording to one study. (Too bad we came on the scene 10,000 years too early – a cosmic blink, really – because having those SMBs whipping around each other in a tight orbit just prior to the ultimate swallow would have been made-to-order for gravitational wave astronomy).

These numbers sound like humongous amounts of mass until one remembers that a single galaxy consisting of ordinary stars, gas and dark matter like ours weighs in at between 600 billion and a trillion soilar masses, which means that the total mass of our galaxy is between 150,000 and 250,000 greater than the ‘paltry’ 4 million-solar mass SMB at the core of our galaxy. The total mass of giant elliptical galaxies like M87 (that would include the dark matter) could be up to 200 times higher than our galaxy, which would be up to 30,000 times greater than even its 6.6 billion solar mass SMB. These are of course only rough estimates, but they probably reflect a reasonable upper bound in the reality.

In any case, an 18 billion-sun SMB can have been produced by the merger of only 3 M87-class SMBs, so its really not all that surprising to find one that size. The principle of medocrity suggests that we’ll probably find one that’s even more massive, given that there are at least 10 million ‘Big Chief’ galaxies (that is, of M87 or OJ 287 caliber) out there to examine.

@ Robert #1, Gary Ansorge #2…

Actually, there may be at least a temporary stop-gap upper limit to the mass of supermassive black holes of roughly 10 billion solar masses, give or take an order of magnitude. One study suggests that active quasars (SMBs that are being fed gas) blow out the gas of their host galaxies, they starve themselves so that the dominant method for subsequent growth becomes SMB mergers. But that basically characterizes whats been going on within the last 13.7 billion years. If the universe continues to expand long enough (and cosmic acceleration continues unabated but doesn’t rip gravitationally-bound galaxy clusters containing thousands of galaxies apart) then those galaxsy clusters would inevitably all merge into a single beast through gravitational radiation, and given even more time, all the bound dead stellar end-states and even the dark matter would likewise be swallowed up, leading to ULTRA-massive SMBs potenially weighing as much as entire galaxy superclusters.

Now, the largest known supercluster in the nearby universe is Shapley Concentration, itself composed of at least 25 galaxy clusters within a volume comparable in size to the more famous Virgo Supercluster. It’s been implicated to be at least partially responsible as the mysterious “Strange Attractor” which seems to be drawing streams of galaxies in our neck of the woods, including our Local Group in that general direction (actually, the general expansion-acceleration of the universe is being noticably RETARDED in that direction). A total mass of 5×10^16 solar masses has been suggested for the Shapley Concentration, but a mass of more than 10^17 solar masses seems to be required to induce the apparent Attraction involved. But if 10^17 solar masses is an upper limit to gravitationally-bound superclusters that don’t get ripped apart by cosmic acceleration, then that figure would represent something like a potential upper-limit for resulting Ultra-massive black holes after having swallowed everything within their grasp…that is, about 100 million billion solar masses.

With an estimated 10 million superclusters in our CURRENTLY observable universe, it means that our observable universe would have up to 10 million of those beasts – if cosmic acceleration continues to call the shots – all gravitationally disconnected from each other. However, if for whatever strange reason cosmic acceleration slows, stops, or even reverses itself (and there ARE hypothetical cosmological models that take those possibilities into consideration) and the universe is granted unlimited time, then the upper mass limit is accordingly raised. If all the mass of the currently observable universe – counting just baryonic (‘ordinary’) matter and non-baryonc (‘dark matter’) and assuming that the universe is near critical density – was piled into a single black hole, the result would be 3.35 x 10^23 solar masses.

So, anyway, yeah, theoretically, there is no upper limit, but practically speaking, there HAS to be a limit somewhere, if one counts everything in the universe that can conceivably go into a black hole.

As a matter of fact, some cosmological models actually characterize our observable universe AS a black hole as seen from the innards…and which propose that our Cosmic singularity lies in our past and our universe appears to us to be expanding because time is reversed in direction within black holes. The actuality may not be quite that simple; just sayin’ that some people have looked into that as a potential possibility. So, Matthew, don’t be too frightened: you may already BE in one. On the other hand, that may be plenty reason to be frightened. Existence has that fine print saying some magilla about how the only way to be completely safe is to be non-existent. Just relax and enjoy the view while you’re around, I always say.8I

Dr_cy_coe Says: “Blackholes are supposed to be pointmasses (singularities), so if our mathematical representation of a blackhole is correct and all the mass is indeed confined within a single point, then spaghettification should not occur. Nor should the less massive blackhole desintegrate by tidal forces. So another test of the singularity model should be that these effects are not observed, right?”

Well, yes and no. A ‘black hole’ is actually that region bound by its event horizon, which has a size. The singularity within it is something else, which is why it is called ‘singularity’, distinguishing it from the ‘black hole’. Also, a spinning black hole (and in nature, probably ALL of them spin at SOME rate) does not produce a point singularity, but something more complicated called a ‘ring singularity’. Even so, it is true with the ideal Schwartzschild (non-spinning) case, a point singularity of one infalling BH would not experience a tidal spaghettification as it merged with the singularity of the swallower.

With Kerr (spinning) cases, it gets much more complicated than ordinary visualization based on Euclidean geometry would suggest, because space and time are hideously distorted and even swapped according to a given reference frame, making a real mess of ‘common sense’ notions like finite extension or size in space or time, and theories that invoke additional dimensions beyond the ordinary three spatial ones (like string theory) have to deal with peculiar entities like ‘branes’, any or all of which would behave much differently than our x,y,z,t-trained intuitions can suppose.

I’m hope I’m not too late for anyone to notice my question, but what would the diameter of this black hole be? I found one website that says our Sun, if compressed into a black hole, would be 5908 meters. Does this mean that a black hole with the mass of 6.6 billion Suns would be 6.6 billion times 5908 meters in diameter?

@ J.D.Mack: The radius r of the event horizon of a simple non-rotating zero charge (Schwarzschild) black hole is proportional to its mass M like this:

r = 2GM/c^2

or, to write it out in fussy English language, the radius r of the event horizon is equal to twice the Gravitational Constant G times the mass M divided by the square of the speed of light c. The diameter of the black hole would be twice the result.

The Gravitational Constant is typically expressed as having a value of 6.674^11 cubic meter per square second per kilogram. But you have to make sure that you are using numbers that reflect the same units of measurement across the board, in this case, kilograms for mass, and understand you will get meters for the answer. (You can easily convert them into kilometers or even Astronomical Units as you please…1 AU = 149,598,000,000 meters, BTW).

One solar mass is 1.9891×10^30 kilograms (about 333,000 times the mass of our Earth) so if there are 6.6 BILLION solar masses involved in the M87 black hole…well, I’ll let you figure it out for yourself. Try it! Let us know what you come up with!:)

“Blackholes are supposed to be pointmasses (singularities), so if our mathematical representation of a blackhole is correct and all the mass is indeed confined within a single point, then spaghettification should not occur”

One reason we keep trying to create/discover a truly unified theory of everything is BECAUSE of that pesky singularity. The math says matter gets compressed to infinity but infinity really doesn’t MEAN anything, it just says that some value is increasing w/o limit. We really don’t know what happens inside a black hole, because our physics breaks down when we can’t SEE what the heck is going on. As far as we CAN know, the center of black holes may be inhabited by fairies and unicorns,,,or merely a roiling sea of energy,,,or an entire universe. The minimum size of matter in THIS universe is 10^-35 meters(Planck Length), but that’s just the smallest we can theoretically measure. It may actually go down to the infinitely small. We just can’t KNOW that because our measuring rods are too large.

Oops, so sorry, the value for G somehow slipped its minus sign ….the Gravitational Constant is 6.674×10^-11. That is, the exponent is NEGATIVE 11. A reminder to always double check one’s work, like I did not, to avoid mistakes yes?

Astronomers used Hubble images to look at over 200,000 red dwarfs, and caught 100 of them in the act of flaring. Some of these stars are pretty old, which is surprising, since it was thought they’d calm down with age. They might in general, but some seem able to stay peppy.